Departamento de Morfología y Biología Celular - Grupo SINPOs, Universidad de Oviedo, Oviedo, Spain.
Departamento de Morfología y Biología Celular - Grupo SINPOs, Universidad de Oviedo, Oviedo, Spain; Servicio de Anatomía Patológica, Complejo Hospitalario Universitario, Salamanca, Spain.
Ann Anat. 2022 Aug;243:151955. doi: 10.1016/j.aanat.2022.151955. Epub 2022 May 17.
Small clear synaptic-like vesicles fill axon terminals of mechanoreceptors. Their functional significance is controversial and probably includes release of neurotransmitters from afferent axon terminals. Synaptophysin, a major protein of the synaptic vesicle membrane, is present in presynaptic endings of the central and peripheral nervous systems. It is also expressed in mechanosensory neurons which extend into skin forming sensory corpuscles. Nevertheless, synaptophysin occurrence in these structures has never been investigated.
Here we used immunohistochemistry to detect synaptophysin in adult human dorsal root ganglia, cutaneous Meissner and Pacinian corpuscles and Merkel cell-neurite complexes from foetal to elderly period. Moreover, we analyzed whether synaptophysin co-localizes with the mechano-gated protein PIEZO2.
Synaptophysin immunoreactivity was observed in primary sensory neurons (36 ± 6%) covering the entire soma size ranges. Axons of Meissner's and Pacinian corpuscles were positive for synaptophysin from 36 and 12 weeks of estimated gestational age respectively, to 72 years old. Synaptophysin was also detected in Merkel cells (from 14 weeks of estimated gestational age to old age). Additionally in adult skin, synaptophysin and PIEZO2 co-localized in the axon of Meissner and Pacinian corpuscles, Merkel cells as well as in some axons of Merkel cell-neurite complexes.
Present results demonstrate that a subpopulation of primary sensory neurons and their axon terminals forming cutaneous sensory corpuscles contain synaptophysin, a typical presynaptic vesicle protein. Although the functional relevance of these findings is unknown it might be related to neurotransmission mechanisms linked to mechanotransduction.
小而清亮的突触小泡充满机械感受器的轴突终末。其功能意义存在争议，可能包括从传入轴突末端释放神经递质。突触素是突触囊泡膜的主要蛋白，存在于中枢和外周神经系统的突触前末梢。它也在延伸到皮肤形成感觉小体的机械感觉神经元中表达。然而，突触素在这些结构中的存在从未被研究过。
在这里，我们使用免疫组织化学技术检测了成人背根神经节、皮肤 Meissner 和 Pacinian 小体以及梅克尔细胞-神经纤维复合体中突触素的表达，研究对象从胎儿到老年。此外，我们还分析了突触素是否与机械门控蛋白 PIEZO2 共定位。
在覆盖整个神经元胞体大小范围的初级感觉神经元（36 ± 6%）中观察到突触素免疫反应性。Meissner 和 Pacinian 小体的轴突从估计的妊娠 36 周和 12 周开始对 PIEZO2 呈阳性，一直到 72 岁。突触素也在梅克尔细胞（从估计的妊娠 14 周到老年）中被检测到。此外，在成人皮肤中，突触素和 PIEZO2 在 Meissner 和 Pacinian 小体、梅克尔细胞以及一些梅克尔细胞-神经纤维复合体的轴突中共同定位。
本研究结果表明，初级感觉神经元的一个亚群及其形成皮肤感觉小体的轴突末端含有突触素，这是一种典型的突触前囊泡蛋白。虽然这些发现的功能相关性尚不清楚，但它可能与机械转导相关的神经传递机制有关。
